Methane (CH.sub.4) is an asphyxiant gas that is colorless, odorless, tasteless, and lighter than air. It is practically inert toward sulfuric acid, nitric acid, alkalies, and salts but reacts with chlorine and bromine in light (explosively in direct sunlight). It is soluble in alcohol and ether but only slightly soluble in water. Methane occurs in natural gas and coal gas and from decaying vegetation and other organic matter in swamps and marshes.
Trichloroethylene (CHCl:CCl.sub.2) is a stable, low-boiling, colorless, photoreactive liquid having a chloroform-like odor. It will not attack the common metals even in the presence of moisture. It is miscible with common organic solvents and slightly soluble in water. It is used as a metal degreaser; an extraction solvent for oils, fats, and waxes; a solvent dye; dry cleaning fluid; as well as a refrigerant and heat exchange liquid. It also is used for cleaning and drying electronic parts. The vapor is toxic by inhalation and use as a solvent is not permitted in some states. The FDA has prohibited its use in foods, drugs, and cosmetics.
Methanotrophic bacteria, those that oxidize methane, have been known and studied for the past 85 years. During this period, the basic physiological capabilities of these organisms have been elucidated with their ability to sequentially oxidize methane, in the presence of air, to carbon dioxide and water, being particularly well defined.
In recent years, increased emphasis has been placed on exploiting the physiological potential of the methanotrophs. Areas of interest include bioconversion of methane to alternate and potentially valuable products, such as methyl alcohol, methyl ketones, and formaldehyde, etc., control of methane in coal mine atmospheres, and degradation of environmentally significant low-molecular weight halocarbons like trichloroethylene in liquid and vapor phases. As a result of these interests, development of bioreactor systems allowing more efficient conversion of gases and vapors are of considerable relevance.
Traditionally, production of large amounts of methanotrophic bacteria, as would be required for the above applications, has been accomplished by growing the organisms on methane/air mixtures that are then added to liquid cultures. An inherent limitation of this method is the relatively limited transfer of methane and air to the liquid phase, since the solubility of methane in water is very low. Consequently, these gases are not available to the bacteria in sufficient quantity and, therefore, become rate limiting. Various techniques have been employed to combat this problem including mechanical agitation and sparging of methane/oxygen or methane/air mixtures through the cultures in an attempt to saturate the liquid culture medium with the necessary gases.
One approach to increasing gas delivery to the methanotrophic bacteria is culturing the organisms on inert supports suspended in a gas or vapor phase. In such a system, gas and/or vapor availability to the cells can be increased. As such, it should be theoretically possible to increase methanotrophic gas and vapor removal rates by making the necessary gases or vapors more readily available to the organisms.
Methods to increase rates of CH.sub.4 oxidation by methanotrophic bacteria are of interest for the bioconversion of CH.sub.4 to alternate compounds and for controlling CH.sub.4 levels, for instance, in mine atmospheres. The rate of CH.sub.4 conversion per unit weight of Methylomonas methanica cells has been shown to be higher in gas phase bioreactors than in liquid cultures. Additionally, the effects of kaolin on CH.sub.4 oxidation rates by Methylomonas methanica in both liquid cultures and gas phase bioreactors has been shown experimentally.
Kaolin (China clay) is a white-burning aluminum silicate which, due to its great purity, has a high fusion point and is the most refractory of all clays. It is composed of alumina (Al.sub.2 O.sub.3) and silica (SiO.sub.2).
It is the purpose of this invention to demonstrate the improvement in the oxidation rate of methane by Methylomonas methanica by the addition of kaolin clay to the apparatus.
It is a further purpose of this invention to demonstrate an apparatus that reduces the concentration of trichloroethylene vapor in a gas by cultures of specific methanotrophic bacteria.